1. Field of the Invention
The present invention relates to a method and apparatus for loading a substrate in a semiconductor manufacturing apparatus. More particularly, it relates to a method and apparatus for loading a substrate on a substrate-loading section so that a temperature difference between the substrate and the section becomes smaller in a vacuum-processing chamber.
2. Description of the Related Art
Conventionally, a sputtering apparatus for depositing a thin film on a substrate, a chemical vapor deposition (CVD) apparatus, an etching apparatus for etching a thin film deposited on a substrate using plasma and the like have been well-known. They are semiconductor manufacturing apparatuses for processing a substrate carried into a vacuum processing chamber. In these semiconductor manufacturing apparatuses, films are deposited or films are etched, so it is widely known that originally undesirable films or etching products from the substrate deposit on a processing table loading the substrate.
Next an example of the conventional CVD apparatus will be explained referring to FIG. 9. This CVD apparatus is a cold-wall type vacuum processing apparatus heating only the substrate to be processed. In this CVD apparatus, the vacuum-processing chamber is comprised of a water-cooled chamber 11. The vacuum-processing chamber is provided with a heat reflecting plate 12 and a processing table 13 housing a heating source. The vacuum-processing chamber is structured so that only the substrate to be processed is heated. The processing table 13 is a substrate holder with a top surface serving as a substrate-loading surface. The processing table 13 is provided with three lift pins 14 arranged in a vertically movable structure, for example. A lift pin drive mechanism 15 for raising and lowering the lift pins 14 and a controller 16 for controlling the operation of the lift pin drive mechanism 15 are provided with respect to the lift pins 14. The lift pin drive mechanism 15 is comprised of a support 15a linked with the plurality of lift pins 14, a movable member 15b supporting the support 15a, and a drive member 15c raising and lowering the movable member 15b. The support 15a is arranged passing through the bottom of the vacuum-processing chamber, so the support 15a is covered by a bellows 15d so as to maintain the vacuum seal of the vacuum-processing chamber and deal with the operation of raising and lowering the support 15a. A substrate 10 to be processed is carried into the vacuum-processing chamber by a transport robot (not shown) through a transport gate 17 and is first placed on the raised lift pins 15. Next, the lift pins 14 are made to descend, whereby the substrate 10 is loaded on the substrate-loading surface of the processing table 13. The processing table 13 houses a heater 18 and is heated to a fixed temperature of 600xc2x0 C., for example. Illustration of the mechanism for supplying power to the heater 18, and the control mechanism for measuring the temperature of the heater 18 using a thermocouple and controlling the amount of power supplied by the power supply mechanism are omitted. Note that the above vacuum-processing chamber is provided with turbo molecular pumps 19 and 20, for example, at a side-wall and bottom for evacuating the inside thereof to a required vacuum state. The inside of the vacuum-processing chamber is divided into a top chamber positioned above the processing table 13 and a bottom chamber positioned below it. The turbo molecular pumps 19 and 20 are used to evacuate the top chamber and bottom chamber to the required pressure, respectively.
After the substrate 10 is loaded on the substrate-loading surface of the processing table 13, a heat stabilization time of 180 seconds is waited for allowing the temperature of the substrate 10 to approach the temperature of the processing table 13 and stabilize, then a heat decomposing gas, Si2H6 gas, is introduced from a gas nozzle 21 at a rate of 12 sccm, for example. Due to this, Si films are deposited on the heated substrate 10. The temperature of the inside-walls of the vacuum-processing chamber is adjusted by water circulating in the water-cooled chamber 11 to become about the water temperature, so the Si2H6 gas does not decompose at the walls and consequently no silicon films are deposited. On the other hand, since the processing table 13 is heated to 600xc2x0 C. by the heater 18, silicon films are deposited at this portion. The silicon films deposited on the processing table 13 increase in thickness along with the number of substrates 10 processed.
In the above conventional CVD apparatus, experience has shown that the silicon films increased in thickness along with the number of substrates processed are subject to heat stress produced by the heat expansion of the substrate and easily peel off from the deposited surface.
Referring to FIG. 10, the action of the peeling of the silicon films due to the heat expansion of the substrate will be explained. As explained above, the processing table 13 is heated to 600xc2x0 C. by the heater 18. As opposed to this, the substrate 10 carried into the vacuum-processing chamber by the transport robot and loaded on the processing table 13 is placed on the substrate-loading surface of the processing table at a relatively low temperature compared with the processing table 13. A silicon film 22 is deposited on the processing table 13 and at the outer circumference of the substrate 10. The substrate 10 in this state is heated by the heat from the processing table 13 and rises in temperature too close to the temperature of the processing table 13.
Here, an explanation will be given of the case where the substrate 10 is at room temperature when loaded in the vacuum-processing chamber. The heat from the processing table 13 rapidly heats the substrate 10 loaded on the processing table 13. When the substrate to be processed is a silicon substrate, and if it has a diameter of 200 mm and a thermal expansion coefficient of 4.1xc3x9710xe2x88x926/xc2x0 C., while being heated from room temperature 25xc2x0 C. to 600xc2x0 C., the substrate expands by exactly 200 (mm)xc3x974.1xc3x9710xe2x88x926 (1/xc2x0 C.)xc3x97(600-25) (xc2x0 C.)=0.47 (mm). At this time, the substrate 10 slides on the substrate-loading surface of the processing table 13, so force is applied to the silicon film 22 deposited on the processing table 13 and peeling is promoted.
The silicon film peeled off due to this action scatters over the substrate as foreign particle and causes originally undesirable defects in the substrate.
Therefore, to prevent this peeling, in the past, the practice had been to allow the temperature of the processing table 13 to sufficiently fall, load the substrate 10, then allow sufficient time to heat it to a predetermined temperature.
With this method, however, a large amount of time was required until the substrate 10 reaches the predetermined temperature and therefore the productivity was remarkably reduced.
The above-mentioned problem also arises in a case that the temperature of the substrate is relatively high compared with the processing table being in a cooled state (or a low temperature state).
An object of the present invention is to provide a method and apparatus for loading a substrate in a semiconductor manufacturing apparatus designed to load the substrate on a heated or cooled processing table in a manner by which the temperature difference between the processing table and the substrate becomes smaller so as to prevent peeling of thin films deposited on the processing table.
The method and apparatus for loading a substrate in a semiconductor manufacturing apparatus according to the present invention are comprised as follows to achieve the above object.
The method of loading a substrate according to the present invention is applied to a semiconductor manufacturing apparatus in which a substrate is carried into a vacuum-processing chamber, loaded on a heated or cooled processing table, and then is processed by predetermined processing in a cold-wall type vacuum processing mode. According to the method of loading a substrate, sufficient time is allowed to elapse before loading the substrate on the processing table so that the temperature difference between the processing table and the substrate at the time of lowering the substrate to load it becomes less than a predetermined temperature. As the method for allowing sufficient time to elapse, it is possible to temporarily stop the substrate. By temporarily stopping it in this way, the temperature difference between the substrate and the processing table is made smaller. When the temperature difference between the substrate and processing table becomes smaller and less than a predetermined temperature, for example, less than 150xc2x0 C. in the case of heating, even if the substrate expands due to heat from the processing table, the extent of the change becomes smaller and the peeling of films deposited on the substrate-loading surface of the processing table can be reduced.
The method of loading a substrate according to the present invention has more specific features as follows in the semiconductor manufacturing apparatus having the above configuration. That is, the semiconductor processing apparatus is provided with lift pins for loading the substrate on the processing table and a drive mechanism for raising and lowering the lift pins. In the method of loading a substrate, the substrate carried into the vacuum-processing chamber is placed on the lift pins and the lift pins are made to descend for loading the substrate on the processing table. The substrate carried into the vacuum-processing chamber by a transport robot is transported above the lift pins moved to an ascended position. When the lift pins are made to descend, sufficient time is allowed to elapse so that the temperature difference between the processing table and the substrate at the time required for loading the substrate becomes less than a predetermined temperature, and then the substrate is loaded on the processing table. For example, the substrate may be made to temporarily stop in the middle of its descent so as to make the temperature difference between the substrate and the processing table smaller than a predetermined level.
In the above method of loading a substrate, preferably the substrate is made to temporarily stop during its descent. Further, preferably, when making the lift pins descend and temporarily stopping the descent above the processing table, the position is in the range of 1 to 50 mm above the table. More preferably, in the method of loading a substrate, the substrate is made to descend at a fixed rate of descent and the descent time is in the range of 1 to 360 seconds. Further, in the method of loading a substrate, preferably, when the substrate is a silicon substrate before processing, the descent time is in the range of 60 to 180 seconds. When the substrate is an actual device substrate the descent time is in the range of 1 to 180 seconds. Further, the descent operation of the lift pins is preferably divided into at least two stages.
The method of loading a substrate according to the present invention is characterized by controlling the substrate-loading method so that the temperature difference between the substrate and processing table becomes less than a predetermined temperature when loading the substrate on the processing table. When the processing table is heated, for example, the temperature difference is preferably less than 150xc2x0 C. from the viewpoint of effectively preventing peeling of silicon films deposited on the substrate-loading surface.
Next, an apparatus for loading a substrate (or a substrate loader) according to the present invention is applied to a semiconductor manufacturing apparatus. In this semiconductor manufacturing apparatus, a substrate is carried into a vacuum-processing chamber, and loaded on a heated or cooled processing table installed in the vacuum-processing chamber, and is applied with predetermined processing. It is provided with lift pins for loading the substrate on the processing table and a drive mechanism for raising and lowering the lift pins. The substrate loader is provided with a first thermometer for measuring the temperature of the substrate, a second thermometer for measuring the temperature of the processing table, and a controller. The controller receives the signals outputted from the first thermometer and second thermometer, and controls the operation of the drive mechanism based on the temperature information of the substrate and the processing table. Thereby, the controller causes sufficient time to elapse when lowering the lift pins so that the temperature difference between the processing table and the substrate at the time of loading the substrate becomes less than a predetermined temperature, and then load the substrate on the processing table. The predetermined temperature is preferably 150xc2x0 C. when the processing table is heated.
Next, an explanation will be made about the process leading up to the idea of the method and apparatus described above.
FIG. 5 shows the results of measurement of the number of pieces of foreign particle when repeatedly processing substrates. In FIG. 5, the abscissa indicates the number of substrates processed and the ordinate the number of pieces of foreign particle. In the case of the conventional method of loading a substrate (graph A), it is learned that the number of pieces of foreign particle exceeds 10 when over 2000 substrates are processed. Therefore, the present inventors analyzed the above phenomenon resulting from the conventional method by measuring the number of pieces of foreign particle when changing the temperature of the substrate carried into the vacuum-processing chamber and changing the time until loading the substrate on the processing table.
FIG. 6 shows the results of measurement of the change in temperature of the substrate (silicon bare substrate), after being carried into the vacuum-processing chamber, using a radiant-energy thermometer. In FIG. 6, the abscissa indicates the time elapsed from placing the substrate on the lift pins, while the ordinate indicates the temperature of the substrate measured using the radiant-energy thermometer. Here, the time shown by the symbol C in FIG. 6 is the time at which the substrate is loaded on the processing table. In FIG. 6, the graph D shows the change in temperature in the case of a silicon bare substrate (silicon substrate before processing), while the graph E shows the change in temperature in the case of an actual device substrate (substrate before processing other than silicon or processed silicon substrate). From FIG. 6, it is learned that the temperature of the substrate 10 is not more than 400xc2x0 C. at the time C when the substrate is loaded on the processing table. In the graph D, the temperature exceeded 400xc2x0 C. in about 120 seconds and stabilized at about 180 seconds. In the graph E, the temperature rose about 5 seconds after loading. The range of measurement of the radiant-energy thermometer (optical pyrometer etc.) used here is from 400xc2x0 C. to 700xc2x0 C. A temperature of not more than 400xc2x0 C. cannot be measured. Note that the characteristic shown by the graph D in FIG. 6 changes according to the thickness of the films deposited on the substrate. For example, if the film becomes thick, sometimes about 360 seconds is required until a stable state is reached.
FIG. 7 shows the results of measurement of the number of pieces of foreign particle when changing the time from when a substrate is placed on the lift pins to when it is loaded on the processing table after a sufficient silicon film is deposited on the processing table after repeated processing of substrates. The time until loading the substrate on the processing table was changed by stopping the descent of the lift pins at a position close to the processing table. In FIG. 7, the abscissa indicates the holding time showing the time until loading, while the ordinate shows the number of pieces of foreign particle. From FIG. 7, it is learned that when the holding time is not less than 120 seconds, the number of pieces of foreign particle becomes not more than 10.
From the above measurement results, it is learned that when loading the substrate on the processing table, there are a large number of pieces of foreign particle when the difference in temperature between the substrate and processing table is large. Based on these measurement results, the present invention, as explained above, proposes the method of loading the substrate on the processing table after the temperature of the substrate sufficiently approaches the temperature of the processing table when the temperatures of the substrate carried into the vacuum-processing chamber and the processing table for loading it remarkably differ, and the apparatus for working the method.